The molecules in this drop have different structures on either of their ends. The end of one molecule is attracted to only one end of a neighbor molecule, and repelled by the other. The molecules behave a little like magnets, except that it’s a chemical attraction that lines them up instead of magnetic fields.
Because of the interaction between the molecules’ ends, they form drops built of layers – leading to these pretty physics pictures.
If there is only enough material in the droplet to for a single layer, it turns into a pancake like the picture below.
In case you’re wondering why you’ve never seen terraced drops, it’s because it only happens for long molecules in very tiny drops. The drops in these images are ten or twenty millionths of a meter across. The researchers took the pictures with a high resolution atomic force microscope.
The images come from an article by Andrew B. Croll, Michael V. Massa, Mark W. Matsen, and Kari Dalnoki-Veress of McMasters University in Ontario and the University of Reading in the UK. It was published today in the journal Physical Review Letters.